In many areas of application today, the transmission of information of any kind is achieved by means of digital data units. The form of the data units is suitably defined for the transmission medium, and is often standardized as well. Examples in this regard are the cells of the Asynchronous Transfer Mode (ATM), or the frames of a Metropolitan Area Network (MAN). The transmission media are designed so that the information from several sources can simultaneously utilize the same physical transmission device. This immediately results in the dilemma of optimum utilization. It consists in having the available capacities for the transportation of digital data units make good use of predetermined transmission devices such as lines, switching units, multiplexers etc., but on the one hand must take obstructions and outages into consideration without any fees, and on the other not restrict the users (sources) too heavily or block them arbitrarily. The problem is defused by reaching arrangements with the users regarding the modalities of the transmissions. If it must be possible to test the maintenance of the agreement on the side of the transmission device, and to impose fines if necessary, a parameter monitor is required at an interface, either at a user or a network interface, mainly known in the literature under the English concept of "usage parameter control" and "policing". A parameter monitor with the respective consequential measures, particularly the discarding of cells, can be useful or necessary irrespective of an agreement with the user, for example if it is necessary to protect a switching unit from overload.
Upon an offense against the agreement, the parameter monitor responds with a discrimination of the non-conforming data unit, usually discarding it or marking it for special treatment or removal later on. It is also possible for several adjacent data units to be discriminated. One or more adjacent discriminated data units are marked as a block of discriminated data units. The response time from one block of discriminated data units to the next is the decisive factor in evaluating the function of the parameter monitor. It is further interesting to know how many data units are affected. It is relatively easy to determine with the parameter monitor itself at what point in time a discrimination of a non-conforming data unit takes place, and how many successive data units are discriminated. However, these additional functions are probably not integrated into the respective parameter monitor, because of considerations of cost-effectiveness on the one hand--the functional evaluation is only used sporadically--and because of the lack of independence on the other. The response time and the number of discriminated data units should rather be determined at a different place in the network. For example, an ATM switching unit can contain a parameter monitor at the inlet, however the measurement to determine the function of the parameter monitor takes place at the outlet of a network interface located at a distance from the switching unit. However, this produces the difficulty that it is neither possible to measure a point in time at which a cell was discarded (since it no longer exists), nor to count how many cells were discarded.
Therefore, the task exists to present a method which makes it possible to perform parameter monitoring of the stream of digital data units arriving at a determined place in the digital network, which acts on the response time of another, possibly far removed place in the network, and to determine the number of discriminated data units.
The method of the invention fulfills the task in that it measures a lower and an upper time barrier at a fixed place in the network, at which the response time is located during that time. The process first receives the missing information about the drop-out of one or more data units from the continuous monitoring of the identification numbers carried by the data units. By comparing the incoming sequence with the sequence of identification numbers known from the agreement, not only the lack of a data unit but also the number of missing data units can be determined. Subsequently, the point in time of the arrival of the last conforming data unit before a block of discriminated data units can be determined, as well as the first conforming data unit that follows it. Together with the starting time determined during the initialization, it provides a measurement of both barriers of the response time at the measurement place.
The method, which comprises the initialization step, the repeated data input steps and the storage step after a gap has been detected in the sequence of data units, has the advantage that only very few operations need to be performed for each incoming data unit. For the most frequent case of repeated data input, a number extraction, a total number comparison, an increment and a subtraction of a constant from the actual time are sufficient. Only two further subtractions need to be made before the storing.
The method is best suited for immediate repetition in that the first non-discriminated data unit after a gap is used for the renewed initialization. Only one other increment and one other subtraction are needed with each storage. This constant and gapless acquisition of the lower and the upper barrier of the response time as well as the number of discriminated data units makes it possible to directly evaluate the measured values statistically. If additional statistical measurements are made in the stream of data units, such as perhaps the average rate (data unit per time unit), time delay fluctuations etc., and are also used in the above mentioned evaluations, the expert in this field has the ability to make conclusive connections, for example through a time sequence analysis or the evaluation of histograms.
During initialization, the starting time is preferred as the difference between the actual time, at which the first non-discriminated data unit arrives, and its time stamp. The time stamp is an indication of the time, carried by the data unit, at which the data unit was treated in a certain way at the source--was transmitted for example. The time stamp in each data cell refers to the same processing point in time. The starting time corresponds approximately to the transmission delay of the data unit. The acquisition of this starting time can also be very conclusive for the statistical evaluation; although for measuring places far removed from the parameter monitor, for example on another continent, the starting time is very large, which could be detrimental. Therefore, a variation in the initialization provides for reducing the difference for determining the starting time by a constant amount, for example by the minimum value of the transmission delay. Such an adaptation of the starting time can also be directly considered in the time stamp.